The objectives are a) to define the mechanism of activation of lipoprotein lipase by synthetic peptide fragments of apolipoprotein C-II, and b) to demonstrate mechanisms of transfer of fatty acids from the surface of triacylglycerol-rich lipoproteins to the endothelial cell surface. Specific experiments are a) to identify which amino acids between residues 55-74 sequence of apoC-II are necessary to activate lipoprotein lipase; b) to demonstrate if fatty acid limits the extent of triacylglycerol hydrolysis; and c) to determine whether or not there is lipoprotein lipase-dependent fusion of the surface film of the triacylglycerol-rich substrate with the endothelial cell membrane. Hydrolytic action of lipoprotein lipase is the only mechanism by which plasma triacylglycerol originating both from the diet and from the liver can be released for uptake by non-hepatic cells. Understanding this key step in lipid metabolism is essential, since concomitant generation of cholesterol-rich remnants at the arterial endothelial surface may have a role in the initiation of atherosclerosis.